Not Applicable
This invention has been created without the sponsorship or funding of any federally sponsored research or development program.
The present invention relates generally to an improvement in a gas chromatograph and specifically to the separation column portion of the gas chromatograph.
A gas chromatograph (GC) is an analytical instrument that takes a gaseous sample, and separates the sample into individual compounds, allowing the identification and quantification of those compounds. The principal components of a typical gas chromatograph are the following: an injector that converts sample components into gases, and moves the gases onto the head of the separation column in a narrow band; a separation column (typically a long, coiled tube) that separates the sample mixture into its individual components as they are swept through the column by an inert carrier gas, the separation being based on differential interactions between the components and an immobilized liquid or solid material within the column; a detector that detects and measures components as they exit the separation column; and a data display.
Typical modern GC instruments are configured with a heated-block xe2x80x9cflash evaporatorxe2x80x9d type injector, a long capillary tube column, an oven housing the column to maintain and to change the column""s temperature in a predictable and reproducible fashion, a detector, and a computer with dedicated hardware/software to process the data collected. Conventional GC instruments can be modified by using different columns (different lengths, different inner diameters, different sorbent phases, and different phase thickness); different detectors; and different data management systems.
Gas chromatographs are used to measure various gas or vaporizable species in a gas or liquid sample. A portion of the gas or liquid sample is received in an inlet of the gas chromatograph. The gas sample is moved through a column which has an interior that is lined with one of any number of known materials, depending on the particular application or gas chromatograph being used, the column separates the larger and smaller molecules in the gas sample. Thus, the gas sample exits the column in such a manner that the first gas species out of the column is the one with the smallest and lightest molecules (a typical example is helium), while the last species is the one with the largest and heaviest molecules. The length of the column varies with each application. Typically, however, where there are a large number of species which the chromatographer desires to separate out from a single gas sample, the column must be quite lengthy.
The gas exiting the column is directed to a detector which detects the various gas species in the sample, as they exit the column. The detector, in turn, provides an output signal indicative of those gas species. The different sample components are therefore retained for different lengths of time within the column, and arrive at the detector at characteristic times. These xe2x80x9cretention timesxe2x80x9d are used to identify the particular sample components, and are a function of the type and amount of sorbtive material in the column, the column length and diameter, the carrier gas type and flow rate, and of the column temperature. In order to have repeatable retention times, the column temperature must also be repeatable. Because a gas chromatograph must operate in a range of ambient temperatures, the gas chromatograph must be controllably heated or cooled.
The current, widely used state of the art in capillary gas chromatography utilizes a gas chromatograph (GC) with an oven that heats a polyimide or metal clad fused silica tube coated with a variety of coatings (mostly polysiloxane based coatings). The oven uses a resistive heating element and a fan circulates heated air in the oven that is integrated into the GC and not the column. The column is cooled by opening vents in the oven, turning off the resistive heating element, and using forced air cooling of the column with ambient air or cryogenic coolent such as liquid carbon dioxide or liquid nitrogen. The disadvantage to the oven heating and cooling technology is that much more mass that is not central to the chromatographic process is heated and cooled than is necessary. Only the column (and the sample introduction and detection devices attached to the inlet and outlet of the column) need to be heated, and generally only the column needs to be cooled. As such, the current state of the art wastes energy, and is limited in its practical heat up (25-75xc2x0 C./min) and cool down rates due to all the extra mass (oven walls, column hangers) that needs to be heated and cooled. Additionally, oven and column cool down rates slow exponentially the closer you get to ambient temperature if using ambient air to cool the oven. It also heats up the environment when cooling, resulting in additional air conditioning costs for laboratories. Alternatively, faster cooling and sub-ambient beginning temperatures can be achieved using cryogenic oven cooling, but this results in additional cost from the consumption of cryogen.
An alternative technology utilizes a metal sheath of unknown composition and resistance to heat a capillary GC column. The column is threaded into the metal sheath, and then the sheath is resistively heated during the chromatographic process, resulting in more rapid heating rates (20xc2x0 C./sec) and more rapid cooling, because of the lower mass that needs to be heated and cooled relative to the oven heating technology described above, with significant efficiency gains ({fraction (1/20)}th of the analysis time). The technology is currently marketed under the name EZ Flash(trademark). U.S. Pat. No. 5,808,178 makes specific reference to resistive heating of a column within a sheath that is separate from the column, not actually integrated into the column structure.
U.S. Pat. No. 5,601,785 makes reference to a connector that would interface with a cartridge column, but the cartridge column is actually a conventional capillary encased in a smaller oven space.
U.S. Pat. No. 5,856,616 is similar to U.S Pat. No. 5,601,785 and the column is also separate from the heating device (a sleeve).
In U.S. Pat. No. 6,068,604, there is mention of a cartridge column and a column on a microchip with a heater attached to the outside of the column. There is no mention of incorporating the heating mechanism into the substrate of this chip in this patent, no mention of how to connect two halves.
Counter flow, gradient heating is as described in U.S. Pat. No. 4,923,486.
In addition to the capital cost of the heating and cooling components of prior art chromatographs, the components are expensive to run. Also, considerable time is required from changing from the heating mode to the cooling mode and back to the heating mode. These and other difficulties experienced with the prior art chromatographs have been obviated by the present invention.
It is, therefore, the principal object of the invention is to provide a separation column for a gas chromatograph which has an integral resistive heating component.
Another object of the present invention is to provide a separation column for a gas chromatograph which has an integral resistive heating and cooling component.
A further object of the present invention is to provide a separation column for a gas chromatograph which has a heating or a heating/cooling component which is relatively simple, relatively inexpensive to operate and is capable of changing temperature quickly and efficiently.
Still further objects of the invention are methods of making a separation column that has an integral resistive heating or resistive heating/cooling components.
A separation column for a gas chromatograph that includes a block of electrically insulating material having a channel located between two strips of thermoelectric material spaced from the channel by strips of electrically insulating material. Electrodes are connected to opposite ends of the strips of thermoelectric material. More specifically, each strip of thermoelectric material has two layers of dissimilar material to enable the strips to provide selective heating and cooling depending on the direction of current flow through the strips.